How do we know that wasn't purely a financial cost-benefit decision?
You'd think if there was such a contract, it would have been mentioned at least one in the many emails and document that leaked and many of which got their own dedicated news articles and topics.
But absolutely nothing on that front.
Microsoft wanted to go to District of Colombia, FTC wanted to go to Northern California where the same court and judge was already overseeing the Gamers vs Microsoft lawsuit.
So it was FTCs ask to stay in the same place where the same judge was already working on a related case.